Urban areas tend to have higher smog concentrations, but most gases aren't known for their tendency to avoid travel and diffusion. Emissions have non-local effects. Some might even say global.

Additionally, gas taxes are about the most straightforward road use fee right now.

Still, non-metro areas tend to get a break. Never understood exactly why but my theory is either additional county/muni taxes, or real estate tends to be cheaper and with it station overhead. This goes out the window if it's an isolated refill chance, though, in which case it's whatever the market will bear.

Don’t fret, it was $5.09 here a couple years ago. And we don’t even have the high fuel taxes :/

Without getting too far off topic: I sincerely wish we had higher taxes on fuel in the rest of Canada (and commensurate increase in relief for lower income folks whom it would disproportionately affect). Everyone complains about the price of gas, but no one cares to change their behaviour and purchasing habits in response. I drive the smallest, most fuel efficient hatchback I could buy 8 years ago, and intend to buy an electric car whenever I move on from this one. I do it for environmental reasons, but the economics don't hurt, either! I've saved 4000+ liters of gas compared to the SUVs/MUVs that most people buy these days.